Planographic plate-making process and sheets

ABSTRACT

PROCESS FOR MAKING PLANOGRAPHIC PRINTING PAPER IN AN CONTINUOUS OPERATION ON A PAPER-MAKING MACHINE. A PAPER WEB IS FORMED FROM AN AQUEOUS SLURRY AND DRIED TO THE POINT THAT IT CONTAINS FROM ABOUT 5% TO ABOUT 30% MOISTURE AND IS SELF-SUPPORTING. A COATING OF INSOLUBILIZING SIZING COMLPOSITION, COMPRISING A HYDROPHILIC FILM-FORMING BINDER MATERIAL SUCH AS POLYVINYL ALCOHOL IS APPLIED TO BOTH SIDES OF THE WEB, THE SIZED WEB IS HEATED SUFFICIENTLY TO DRY THE SIZING COMPOSITION TO THE POINT THAT IT IS NON-TACKY, BUT WITHOUT SUBSTANTIAL INSOLUBILIZATION OF THE SIZE, AND THEN A COATING OF SELF-INSOLUBILIZING PLANOGRAPHIC COMPSOITION, COMPRISING 1 PART BY WEIGHT OF A HYDROPHILIC FILM-FORMING BINER MATERIAL, SUCH AS POLYVINYL ALCOHOL AN INSOLUBILZING AGENT SUCH AS GLYOXAL, AND FROM 4 TO 8 PARTS BY WEIGHT OF A FILLER, SUCH AS CLAY, SILICA, OR A MIXTURE OF BOTH, IS APPLIED TO AT LEAST ONE SIDE OF THE WEB. FINALLY THE COATINGS ARE INSOLUBILIZED TOGETHER AND THE WEB IS CALENDERED, ALL ON THE PAPER-MAKING MACHINE.

July 13, 1971 u. A. NEWMAN 3,592,

PLANOGRAPHIC PLATE-MAKING PROCESS AND SHEETS Filed Jan. 21, 1969 INVENTOR.

fiouylas A. Mary/ 200 BY WMM United States Patent ()ifice 3,592,730 Patented July 13, 1971 3,592,730 PLANOGRAPHIC PLATE-MAKING PROCESS AND SHEETS Douglas A. Newman, Glen Cove, N.Y., assignor to Columbia Ribbon and Carbon Manufacturing Co.,

Inc., Glen Cove, NY.

Filed Jan. 21, 1969, Ser. No. 792,425 Int. Cl. D21f 11/00 US. Cl. 162137 7 Claims ABSTRACT OF THE DISCLOSURE Process for making planographic printing paper in a continuous operation on a paper-making machine. A paper web is formed from an aqueous slurry and dried to the point that it contains from about to about 30% moisture and is self-supporting. A coating of insolubilizing sizing composition, comprising a hydrophilic film-forming binder material such as polyvinyl alcohol is applied to both sides of the web, the sized web is heated sufiiciently to dry the sizing composition to the point that it is non-tacky, but without substantial insolubilization of the size, and then a coating of self-insolubilizing planographic composition, comprising 1 part by weight of a hydrophilic film-forming binder material, such as polyvinyl alcohol an insolubilizing agent such as glyoxal, and from 4 to 8 parts by weight of a filler, such as clay, silica, or a mixture of both, is applied to at least one side of the web. Finally the coatings are insolubilized together and the web is calendered, all on the paper-making machine.

The present invention relates to the field of planographic printing plates and more particularly to a novel method for making relatively inexpensive paper which is suitable for use for short-run and medium-run planographic printing purposes. Conventional planographic printing plates are produced in two separate operations. In the first operation the paper base is produced on a paper-making machine from an aqueous pulp slurry, dried, coated with sizing composition, dried again and then calendered to form the paper base which is wound on a roll for aftertreatment in the second operation. The time lapse between these operations varies and heretofore it was not appreciated that a variation in this time lapse gave rise to a variation in the properties of the plates produced. In the second operation the paper base is unwound from the roll and coated with an aqueous planographic composition, dried and calendered and rewound on a roll for cutting into paper plates of the desired dimensions.

One of the most common problems with planographic printing plates is their tendency to curl or roll, which makes them difficult to manipulate and image, particularly in automatic imaging machines. This problem can be controlled but this requires the application of curl-preventing coatings on the back of the plates, and other additional steps which add to the expense of preparing the plates.

Another important problem which increases the cost of preparing planographic plates is the necessity for providing an adequate hydrophilic barrier over the entire surface of the plate so that the normal affin ity of the paper base for oleous printing ink is completely masked. This requires that one or more hydrophilic barrier layers be applied over the paper base prior to the application of the planographic printing layer. These layers impart curl to the paper base and add to the overall cost.

I have discovered that very useful planographic printing plates having little or no tendency to curl may be produced in an inexpensive manner in a rapid continuous process which results in printing plates of excellent uniformity.

The accompanying drawing illustrates one form of apparatus suitable for carrying out the present process. As shown in the drawing, a semi-dry, self-supporting web of paper 10 proceeds on its passage through the papermaking machine over roller 11 and in the nip of sizecoating rollers 12 and 15, each of which is provided with a continuous supply of insolubilizing sizing composition from size tanks 13 by means of application rollers 14 and 16, respectively. The web is uniformly coated on both sides with the sizing composition and is next passed over drying drums 17 and 18 which are sufiiciently hot to partially dry the sized web and render it non-sticky but insuificient to fully dry and insolubilize the size coats.

The sized web proceeds over idler rollers, 19, 20 and 21 and in the nip of planographic coating rollers 22 and 25. Rollers 22 and 25 are provided with a continuous supply of self-insolubilizing aqueous planographic composition from planographic tanks 23 by means of application rollers 24 and 26. Doctor blades may be provided to regulate the thickness and weight of the applied coatings.

The web, coated on both sides with a planographic coating, is next contacted with a series of drying drums 27 to 30 to completely dry and insolubilize the sizing coatings and the planographic layers simultaneously. The dried web is then passed over rollers 31 and 32 which are preferably heated rollers which insure complete drying of the web.

Next the dried web is passed in the nip of calendering rolls 33 and 34 which provide the planographic layers on each side with a smooth even surface. The calendered Web is finally passed over idler roll 35 and proceeds to take-up roll 36 for subsequent final processing such as cutting into sheets of the desired length.

The present invention is based on the essential discovery that the manufacture of planographic printing plates in a single continuous operation results in stable, uniform, unitary-type plates whereas the production of plates in the conventianal two-step process gives rise to unnecessary problems and disadvantages which can only be overcome at added expense.

In the conventional process the paper base is first prepared as a complete product which is suitable for a variety of uses. It generally contains wet-strength additives and sizing, and is calendered to a hard, smooth finish and is wound on a roll where it ages until needed. It sets on the roll as the sizing gradually insolubilizes and thus the paper develops a curl. In the second operation the planographic layer is applied either directly to the paper, or more commonly, over a hydrophilic barrier layer. These layers bond fairly well to the smooth paper surface but do not really integrate therewith, so that they adhere as separate, individual layers having their own moisture-absorption properties and expansion and contraction properties. These will differ from the corresponding properties of the paper web, and the properties of paper webs will differ from each other depending on the age of the web and the ambient conditions and duration of its storage.

The present invention obviates these problems and disadvantages by producing planographic printing plates in such a manner that paper, as such, is not produced independently of the coatings which render it suitable for use as a planographic printing plate. I have discovered that the manufacture of planographic printing plates in a single continuous operation results in unitary structures having unitary stable properties of flatness, uniformity, moisture retention and oil rejection.

According to the present process, an aqueous paper slurry is prepared in conventional manner from beaten fibers of wood pulp, and wet-strength additives such as melamine-formaldehyde resin are preferably included. The slurry is processed on a paper-making machine to the point that it is compacted as a self-supporting web and dried to the point that it contains at least by weight of moisture and up to 3% by weight of moisture. The moist web is then coated on both sides with an aqueous, insolubilizing, hydrophilic sizing composition which penetrates the web because of its moist condition and the water-loving nature of the sizing composition. This may be accomplished by means of a conventional size tub as illustrated in the drawing.

The sized web is then heated sufficiently to dry the sizing composition to the point that it is non-tacky, though still moist. Apparently at this point the insolubilization reaction is initiated, if an insolubilizing agent is present rather than being supplied by the planographic composition, but complete insolubilization does not occur until the web is completely dried.

Next the moist sized web is coated on one or both sides with a uniform lightweight layer of aqueous, self-insolubilizing planographic composition which is hydrophilic and therefore penetrates the non-insolubilized moist size coating to some extent and becomes integrated therewith. At this point the web is heated sufliciently high to completely dry the paper web, size coats and planographic layer or layers so that insolubilization of the integrated size and planographic layers occurs simultaneously. Thereafter the planographic surface or surfaces of the web are calendered to render them smooth and uniform, and the Web is wound on a take-up roll for final processing such as cutting into sheet lengths of the desired dimensions.

One of the most important uses for plates of the present type is for short-run system forms which generally are employed to produce a small number of copies and are then discarded. Aside from being more economical for such use, the present plates function better in those applications where only a portion of the imaged subject matter of the plates is reproduced on some of the copies and all of the imaged subject matter is reproduced on the rest of the copies. This is achieved by separating the inking roller from the plate surface at regular intervals to prevent a portion of the images on the plate from being inked and then permitting continuous contact when all of the subject matter is to be inked and reproduced.

With conventional plates the later copies, containing all of the subject matter, are of uneven tone. The images previously reproduced are dark While the images repro- I ducing for the first time are very light in density. However, this disadvantage is not encountered with the present plates for some reason, apparently because of the ability of the present planographic surface layers to absorb and retain water to a greater degree than previous plates having greater water-resistance. Since the background areas of the present plate surfaces are more water-retentive, the images are able to accept and retain a greater amount of printing ink from the start and therefore uniformly dark images are produced from the first copy. Conventional plates having water-barrier layers and heavier planographic coatings are more water-resistant when initially wetted and thus do not produce dark printed images until the plate has been run several times. The first few printed copies are light and are discarded.

The present plates are also suitable for medium-run use, up to 1000 copies at most, but the short-run utility, up to about 200 copies, is preferred because of the limited waterresistance of the lightweight planographic layers.

The weight of the paper stock useful according to this invention will vary depending upon the end use for which the plate is intended. For short-run plates the paper, prior to sizing, is produced in a weight of from about pounds per ream up to about 30 pounds per ream, a ream equalmg 500 sheets x 38" in dimensions 3300 square feet 1b of Web. For medium-run plates the paper may be produced in a weight up to about 60 pounds per ream, and wet-strength resin is included in the furnish.

The sizing composition is applied to each side of the paper web in a weight of from about 2 to 5 pounds per ream and preferably about 3 pounds per ream. Conventional self-insolubilizing sizing compositions may be used comprising a hydrophilic film-forming material and a hardening agent. Polyvinyl alcohol is preferred, but starch, casein, zein, gum arabic, gelatin, carboxymethyl cellulose, and the like, are also suitable. Suitable insolubilizing agents vary depending on the particular filmforming material but include the following combinations: glyoxal, dimethylol urea or other formaldehyde source to insolubilize polyvinyl alcohol, ammoniacal casein or hydroxyethyl starch or gelatin or other aldehyde-insolubilized colloid; metal salts such as zinc acetate or copper sulfate to insolubilize carboxymethyl cellulose, and the like.

Actually the insolubilizing agent or hardener for the size coatings may be applied as part of the planographic coatings since the latter permeate the uncalendered size coats and since both coatings are insolubilized and hardened together. In all cases an insolubilizing agent for the size coating is present, either initially in the sizing composition or as an ingredient of the self-insolubilizing planographic composition. In the latter case it is preferred that both coatings are insolubilized by the same material, such as glyoxal, so that a single hardener can be present in the planographic composition in a sufficient amount to insolubilize both coatings.

The sizing composition may also contain a filler such as clay, silica, zinc oxide or the like in an amount ranging rom about /2 to 2 parts per part of hydrophilic filmforming material.

The planographic composition is applied over the size coating in a weight of from about 2 to 5 pounds per ream and may comprise any conventional self-insolubilizing planographic composition containing 1 part by weight of a hydrophilic film-forming binder material and from 4 to 8 parts by weight of a filler such as colloidal silica, clay or the like, or mixtures thereof. The binder may be heatinsolubilized or the composition may contain an insolubilizing agent such as an aldehyde donor, a metal salt or other reactive material which converts the binder from soluble to insoluble condition. Suitable hydrophilic binders include polyvinyl alcohol, sodium carboxymethyl cellulose, sodium alginate and other conventional binders capable of producing planographic layers having the required hydrophilic-oleophilic balance.

The following procedure is set forth by Way of illustration and should not be considered limitative with respect to the specific materials, weights and conditions recited.

A paper furnish is prepared in conventional manner from beaten pulp in amounts sutficient to form a final web weighing about 20 pounds per ream of 500 sheets, 25 x 38" in dimensions. The furnish may have melamineformaldehyde resin added thereto in order to impart wet strength to the web. The furnish is processed through a paper-making machine in which the pulp is collected in sheet form on a screen and the water is filtered away. The sheet is contacted with drying cylinders and heated sufficiently to reduce the moisture content to about 10% by weight and produce a compacted self-supporting paper web.

The moist web is next passed in the nip of coating rollers which apply about 3 pounds per ream of sizing composition to each side of the web, the composition comprising the following:

Ingredients: Parts by weight Polyvinyl alcohol (10% aqueous solution) 10.0 Glyoxal (40% aqueous solution) 0.25 Clay (60% aqueous dispersion) 4.0 Syton (colloidal silica) 3.0

The coated web is next contacted with drying drums heated to about 300 F. to dry the size coatings to the point that they are not adhesive and still retain some moisture. The duration of heating is brief so that the insolubilization reaction is not permitted to proceed very far but may be initiated.

Next the size-coated web proceeds into the nip of a second set of coating rollers which apply about 3 pounds per ream of planographic composition to each surface of the web, the composition being as follows:

Ingredients: Parts by weight Polyvinyl alcohol (10% aqueous solution) 10.0

Clay (60% aqueous suspension) 8.0 Syton (colloidal silica) 3.0 Glyoxal (40% aqueous solution) 0.5

The coated web is then passed against a series of drying drums heated to conventional paper-making temperatures to dry the web, size coatings and planographic coatings to leave about 5% moisture content and cause the coatings to insolubilize and harden together as an integrated unit which in turn is integrated with the paper web.

Finally the web is contacted with calendering rolls which smooth the planographic surfaces and compress the web, and the web is wound on a take-up roll for final cutting. This winding operation is necessary because of the speed of operation of the paper-making machine. The cutting of the web into sheet lengths is preferably done as soon after winding as possible.

While it is not essential that the present plates carry a planographic printing layer on both surfaces, it is essential that they carry a self-insolubilizable curl-compensating layer on the surface opposite to that carrying the planographic printing layer. According to the preferred embodiment, the curl-compensating layer is a planographic printing layer of the same composition as the printing layer on the opposite surface so that either or both surfaces may be used for printing purposes. Otherwise the curl compensating layer should be tinted for identification purposes and may comprise a coating of a water-applied selfinsolubilizable binder material. The binder material is preferably a hydrophilic material such as polyvinyl alcohol, carboxymethyl cellulose, starch, casein or the like, in combination with a suitable hardening agent.

The hydrophilic nature of the sizing composition applied to both sides of the paper web and integrated therewith improves the printing properties of the present plates by reinforcing the hydrophilic properties of the top planographic layer and masking the fibers of the paper support. Equally importantfithe sizing layers permit the making of erasures and corrections on the planographic layer since the removal of portions of the planographic layer during the erasing operation will merely expose portions of the sizing layer which are also hydrophilic and planographic.

1 claim:

1. Process of producing a web of planographic printing plates in a continuous operation which comprises the steps of:

(a) forming a continuous Web of paper from an aqueous slurry;

(b) drying the web to the point that it retains from about 5% to 30% by weight of water;

(0) applying substantially equal amounts within the range of from 2 to 5 pounds per 3300 square feet of an aqueous insolubiliza'ble sizing composition comprising a hydrophilic film-forming binder material as coatings to both sides of the Web;

(d) heating the sized web sufliciently to dry the sizing composition to the point that it is non-tacky, but without substantial insolubilization of the size;

(e) applying substantially equal amounts within the range of from 2 to 5 pounds per 3300 square feet of aqueous self-insolubilizable planographic compositions comprising 1 part by weight of a hydrophilic film-forming binder material, an insolubilizing agent and from 4 to 8 parts by weight of a filler as coatings over the sizing composition coatings on both sides of the web;

(f) applying heat to dry said web and coatings, and

insolubilizing said coatings together; and

(g) calendering said coated web on both sides to form. a stable, unitary web having planographic printing coatings on both surfaces.

2. Process according to claim 1 in which all of the coatings are applied in an amount of about 3 pounds per 3300 square feet of web.

3. Process according to claim 1 in which the paper web, prior to application of the sizing composition, has a weight of from 10 to 60 pounds per ream.

4. Process according to claim 1 in which the sizing composition is self-insolubilizing due to the inclusion therein of a hardening agent.

5. Process according to claim 1 in which the planographic compositions contain a hardening agent which insolubilizes the sizing composition coatings.

6. Process according to claim 1 in which said planographic composition comprises polyvinyl alcohol, colloidal silica and clay.

7. A web of planographic printing plates produced according to the process of claim 1.

References Cited UNITED STATES PATENTS 1,032,973 7/1912 Wagg 162--184 2,006,392 7/1935 Greider 162184 3,031,958 5/1962 Newman 10l466 3,055,295 9/1962 Perkins 101-466 OTHER REFERENCES Calkin & Witham, Modern Pulp and Paper Making, 3rd edition, 1957, p. 476.

S. LEON BASHOVE, Primary Examiner R. H. ANDERSON, Assistant Examiner U.S. Cl. X.R.

zg;gg UNITED STATES PATENT OFFICE CERTIFKCATE OF CORRECTION Patent No. 3,592,730 Dated y 31, 1971 Inventor-(s) Douglas A wman It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

I. Column 3, line 8, "3%" should read 30% 7 Column 6, line 29, "mm" should read 3300 square feet line Sh, "Bashove should read Bashore Signed and sealed this 11th day of January 1972.

(SEAL) Attest:

EDWARD MFETCHER, JR. ROBERT GOT'ISCHALK Attesting Officer Acting Commissioner of Patents 

